1. Field of the Invention
The present invention relates to a direct-type back light module, and more specifically, to a direct-type back light module with photo sensors for improving the illumination uniformity of the direct-type back light module.
2. Description of the Prior Art
Back light modules are known in the art. The back light module, which is a key element in the fabrication of liquid crystal displays (LCDs), is widely used in monitors, notebooks, digital cameras, projectors and so on. Back light modules are typically divided into two major categories: edge light type and direct-type, wherein the direct-type back light module can provide higher intensity of light by utilizing a plurality of lamps and is thus more suited for large size display panels, such as display panels or TV panels, than the edge light type.
Please refer to FIG. 1 and FIG. 2, which respectively represent a cross-sectional view and an exploded side view of a direct-type back light module 10 according to the prior art. As shown in FIG. 1 and FIG. 2, the direct-type back light module 10 is disposed in a housing 14 under a display panel 12 and comprises a diffuser 16, a metal reflecting sheet 18 installed on side surfaces and a bottom surface of the direct-type back light module 10, and a plurality of parallel lamps disposed in a chamber 22 defined by the diffuser 16 and the metal reflecting sheet 18. Generally, the display panel is a LCD panel, and the housing 14 comprises a plastic shield, aluminum bezel or a metal sheet.
The metal reflecting sheet 18 is employed to upwardly reflect the light generated by the lamps 20, and the diffuser 16 is utilized to evenly scatter the reflected light by the metal reflecting sheet 18, so as to enhance the display efficiency of the direct-type back light module 10. In addition, the direct-type back light module 10 further comprises a diffuser 24 and at least one prism 26. The diffuser 24 is a hazy sheet composed of either polyethylene terephthalate (PET) or polycarbonate (PC), and has a thickness ranging from 0.11 to 0.15 cm, and the prism 26 is employed to reduce the difference of the luminous intensities on the display panel 12 in advance. The quantity and placing order of the diffuser 24 and prism 26 employed are defined by the specification of the direct-type back light module 10.
As previously mentioned, the light generated by the lamps 20 is upwardly reflected by the reflecting sheet 18 and is then scattered by the diffuser 16. By utilizing the diffuser 24 and the prism 26, the scattered light is further scattered to achieve a uniform luminous intensities on the display panel 12. However, the lamps 20 may be produced in different batches and therefore differ from each other in luminous intensities, despite of the fact that the lamp current and the voltage applied on each lamp 20 is the same. As a result, the display quality of the display panel 12 is reduced.
Normally, diffusers with either better diffusing abilities or greater thicknesses are frequently employed to solve this uneven luminous intensity issue on the display panel. Unfortunately, this would lead to a reduced intensity of the scattered light on the display panel that fails the product requirement. As a result, the lamp current applied on each lamp needs to be increased, shortening the product lives of the lamps due to the correspondingly increased power of the lamps during operation.